Schemas

Elliotte Rusty Harold

Software Development 2000 East

Wednesday, November 1, 2000

elharo@metalab.unc.edu

http://www.ibiblio.org/xml/

What are Schemas?

Generically, a document that describes what a correct document may contain
Specifically, a W3C Recommendation for an XML-document syntax that describes the permissible contents of XML documents

About Schemas

Created by W3C XML Schema Working Group based on many different submissions
No known patent, trademark, or other IP restrictions
XML Schema Part 1: Structures: http://www.w3.org/TR/xmlschema-1/
XML Schema Part 2: Datatypes: http://www.w3.org/TR/xmlschema-2/

What's Wrong with DTDs?

Unusual, non-XML like syntax
No data typing, especially for element content
Limited extensibility
Only marginally compatible with namespaces
Cannot use mixed content and enforce order and number of child elements
Cannot enforce number of child elements without also enforcing order. (i.e. no & operator from SGML)

DTDs vs. Schemas

DTDs	Schemas
`<!ELEMENT>` declaration	`xsd:element` element
`<!ATTLIST>` declaration	`xsd:attribute` element
`<!NOTATION>` declaration
`<!ENTITY>` declaration
	`Data types`

Schema versions

Last call working draft from April 7, 2000
Candidate Recommendation October 24, 2000

greeting.xml

<?xml version="1.0"?>
<GREETING>
Hello XML!
</GREETING>

greeting.xsd according to the April 7 Working Draft

<xsd:schema xmlns:xsd="http://www.w3.org/1999/XMLSchema">
 
  <xsd:element name="GREETING" type="xsd:string"/>

</xsd:schema>

Attaching the schema to the document without namespaces

xsi:noNamespaceSchemaLocation attribute on root element
xsi prefix is mapped to http://www.w3.org/1999/XMLSchema-instance URI

For example,

<?xml version="1.0"?>
<GREETING xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="greeting.xsd">
Hello XML!
</GREETING>

Other means of connecting schemas to documents are allowed

Validating the document with Xerces-J 1.2.0

D:\schemas\examples>java sax.SAX2Count -v greeting2.xml
greeting2.xml: 701 ms (1 elems, 1 attrs, 0 spaces, 12 chars)

An Invalid Document

<?xml version="1.0"?>
<GREETING xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="greeting.xsd">
  <P>Hello XML!</P>
</GREETING>

Checking the Invalid Document

D:\speaking\Software Development 2000 East\schemas\examples>java sax.SAX2Count -v greeting3.xml
[Error] greeting3.xml:4:6: Element type "P" must be declared.
[Error] greeting3.xml:5:13: Datatype error: In element 'GREETING' : Can not have
 element children within a simple type content.
greeting3.xml: 781 ms (2 elems, 1 attrs, 0 spaces, 14 chars)

greeting.xsd in the Candidate Recommendation

The namespace URIs have changed.

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="GREETING" type="xsd:string"/>

</xsd:schema>

New XSI namespace

xsi:noNamespaceSchemaLocation attribute on root element
xsi prefix is mapped to http://www.w3.org/2000/10/XMLSchema-instance URI

For example,

<?xml version="1.0"?>
<GREETING xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="greeting.xsd">
Hello XML!
</GREETING>

Validating the document with XSV

http://www.w3.org/2000/09/webdata/xsv

An Invalid Document

<?xml version="1.0"?>
<GREETING xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="greeting.xsd">
  <P>Hello XML!</P>
</GREETING>

Checking the Invalid Document

A More Complex Document

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="song.xsd">
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Complex vs. Simple Types

Complex types can have child elements and attributes
Simple types cannot have children or attributes

A More Complex Schema

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">

  <xsd:element name="SONG" type="songType"/>
 
  <xsd:complexType name="songType">
    <xsd:element name="TITLE"     type="xsd:string"/>
    <xsd:element name="COMPOSER"  type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="xsd:string" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="LENGTH"    type="xsd:timeDuration"/>
    <xsd:element name="YEAR"      type="xsd:string"/>
    <xsd:element name="ARTIST"    type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
  </xsd:complexType>
 
</xsd:schema>

Three main schema elements:

xsd:element declares an element and assigns it a type
xsd:attribute declares an attribute and assigns it a type
xsd:complexType defines a new type

Validating the Song Document

D:\speaking\Software Development 2000 East\schemas\examples>java sax.SAX2Count -v hotcop.xml [Error] hotcop.xml:10:25: Datatype error: java.text.ParseException: Illegal or misplaced separator.

Here's the problem:

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="song.xsd">
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

This is not in the schema time duration format! which is ISO 8601 "PnYn MnDTnH nMnS, where nY represents the number of years, nM the number of months, nD the number of days, 'T' is the date/time separator, nH the number of hours, nM the number of minutes and nS the number of seconds. The number of seconds can include decimal digits to arbitrary precision. An optional preceding minus sign ('-') is allowed, to indicate a negative duration."

Fixed Hot Cop

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="song.xsd">
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>P0YT6M20S</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>
</SONG>

Xerces doesn't get this one right yet!

Primitive Data Types for Schemas

Boolean
String
URIs
Numeric types
Time types
XML types
No money types. However, these can be derived

Numeric Data Types for Schemas

XML Schema Built-In Simple Types
Name	Type	Examples
float	IEEE 754 32-bit floating point number	-INF, -1E4, -0, 0, 12.78E-2, 12, INF, NaN
double	IEEE 754 64-bit floating point number	-INF, 1.401E-90, -1E4, -0, 0, 12.78E-2, 12, INF, NaN, 3.4E42
decimal	arbitrary precision, decimal numbers	-2.7E400, 5.7E-444, -3.1415292, 0, 7.8, 90200.76, 3.4E1024
binary	a binary number made up of zeroes and ones	10000100111
integer	an arbitrarily large or small integer	-500000000000000000000000, -9223372036854775809, -126789, -1, 0, 1, 5, 23, 42, 126789, 9223372036854775808, 456734987324983264987362495809587095720978
nonPositiveInteger	an integer less than or equal to zero	0, -1, -2, -3, -4, -5, ...
negativeInteger	an integer strictly less than zero	-1, -2, -3, -4, -5, ...
long	an eight-byte two's complement integer such as Java's `long` type	-9223372036854775808, -12678967543233, -1, 9223372036854775807
int	an integer that can be represented as a four-byte, two's complement number such as Java's `int` type	-2147483648, -1, 0, 1, 5, 23, 42, 2147483647
short	an integer that can be represented as a two-byte, two's complement number such as Java's `short` type	-32768, -1, 0, 1, 5, 23, 42, 32767
byte	an integer that can be represented as a one-byte, two's complement number such as Java's `byte` type	-128, -1, 0, 1, 5, 23, 42, 127
nonNegativeInteger	an integer greater than or equal to zero	0, 1, 2, 3, 4, 5, ...
unsignedLong	an eight-byte unsigned integer	0, 1, 2, 3, 4, 5, ...18446744073709551614, 18446744073709551615
unsignedInt	a four-byte unsigned integer	0, 1, 2, 3, 4, 5, ...4294967294, 4294967295
unsignedShort	a two-byte unsigned integer	0, 1, 2, 3, 4, 5, ...65534, 65535
unsignedByte	a one-byte unsigned integer	0, 1, 2, 3, 4, 5, ...254, 255
positiveInteger	an integer strictly greater than zero	1, 2, 3, 4, 5, 6, ...

Time Data Types for Schemas

XML Schema Built-In Simple Types
Name	Type	Examples
timeInstant	a particular moment in Co-Ordinated Universal Time; up to an arbitrarily small fraction of a second	1999-05-31T13:20:00.000-05:00
month	A given month in a given year	2000-10
year	a given year	2000
century	a specified century	19
recurringDate	a date in no particular year, or rather in every year	--10-31
recurringDay	a day in no particular month, or rather in every mnonth	----31
timeDuration	a length of time, without fixed endpoints, to an arbitrary fraction of a second	P2000Y10M31DT09H32M7.4312S
date	a specific day in history	2000-10-31
time	a specific time of day, that recurs every day	14:30:00.000, 09:30:00.000-05:00

XML Data Types for Schemas

XML Schema Built-In Simple Types
Name	Type	Examples
ID	XML 1.0 ID attribute type	any XML name that's unique among ID type attributes
IDREF	XML 1.0 IDREF attribute type	any XML name that's used as an ID type attribute elsewhere in the document
ENTITY	XML 1.0 ENTITY attribute type	any XML name that's declared as an unparsed entity in the DTD
NOTATION	XML 1.0 NOTATION attribute type	any XML name that's declared as a notation name in the DTD
language	valid values for xml:lang as defined in XML 1.0	en-GB, en-US, fr
IDREFS	XML 1.0 IDREFS attribute type	a white space separated list of IDREF names
ENTITIES	XML 1.0 ENTITIES attribute type	a white space separated list of ENTITY names
NMTOKEN	XML 1.0 NMTOKEN attribute type	12 are you ready
NMTOKENS	XML 1.0 NMTOKENS attribute type	a white space separated list of name tokens
Name	An XML 1.0 Name	set, title, rdf, math, math123, href
QName	a prefixed name	song:title
NCName	a local name without any colons	title

Assorted Data Types for Schemas

XML Schema Built-In Simple Types
Name	Type	Examples
string	Parsed Character Data; #PCDATA	Hot Cop
boolean	C++'s bool type	true, false, 1, 0
uriReference	relative or absolute URI	http://www.w3.org/TR/2000/WD-xmlschema-2-20000407/#timeDuration, /javafaq/reports/JCE1.2.1.html

A Document with Attributes

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="attribute_song.xsd">
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Declaring Attributes

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <!-- An empty element -->
  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>

  <xsd:complexType name="SongType">
  
    <xsd:element name="TITLE"     type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="PHOTO"     type="PhotoType"  
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="COMPOSER"  type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="xsd:string" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="YEAR"   type="xsd:year"
       minOccurs="1" maxOccurs="1"/>
    <xsd:element name="ARTIST" type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    
  </xsd:complexType>

</xsd:schema>

Element Content

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="nested_song.xsd">
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>
    <NAME>
      <GIVEN>Jacques</GIVEN>
      <FAMILY>Morali</FAMILY>
    </NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>
      <GIVEN>Henri</GIVEN>
      <FAMILY>Belolo</FAMILY>
    </NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>
      <GIVEN>Victor</GIVEN>
      <FAMILY>Willis</FAMILY>
    </NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME>
      <GIVEN>Jacques</GIVEN>
      <FAMILY>Morali</FAMILY>
    </NAME>
  </PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Declaring Complex Types

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="ComposerType">
    <xsd:element name="NAME">
      <xsd:complexType>
         <xsd:element name="GIVEN"  type="xsd:string" 
           minOccurs="1" maxOccurs="1"/>
         <xsd:element name="FAMILY" type="xsd:string" 
           minOccurs="1" maxOccurs="1"/>      
      </xsd:complexType>
    </xsd:element>
  </xsd:complexType>

  <xsd:complexType name="ProducerType">
    <xsd:element name="NAME">
      <xsd:complexType>
        <xsd:element name="GIVEN"  type="xsd:string" 
          minOccurs="1" maxOccurs="1"/>
        <xsd:element name="FAMILY" type="xsd:string" 
          minOccurs="1" maxOccurs="1"/>      
      </xsd:complexType>
    </xsd:element>
  </xsd:complexType>

  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>
  
  <xsd:complexType name="SongType">
  
    <xsd:element name="TITLE"     type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="PHOTO"     type="PhotoType"  
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="COMPOSER"  type="ComposerType" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="ProducerType" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="YEAR"   type="xsd:year" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="ARTIST" type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    
  </xsd:complexType>

</xsd:schema>

Sharing Content Models

PRODUCER and COMPOSER are really the same type.

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="PersonType">
    <xsd:element name="NAME">
      <xsd:complexType>
        <xsd:element name="GIVEN"  type="xsd:string" 
          minOccurs="1" maxOccurs="1"/>
        <xsd:element name="FAMILY" type="xsd:string" 
          minOccurs="1" maxOccurs="1"/>      
      </xsd:complexType>
    </xsd:element>
  </xsd:complexType>

  <xsd:complexType name="SongType">
  
    <xsd:element name="TITLE"     type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="PHOTO"     type="PhotoType"  
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="COMPOSER"  type="PersonType" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="PersonType" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="YEAR"   type="xsd:year" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="ARTIST" type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    
  </xsd:complexType>

  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>
  
</xsd:schema>

Mixed Content

Schemas let you enforce order and appearance of elements in mixed content.

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="mixed_song.xsd">
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>
    <NAME>Mr. <GIVEN>Jacques</GIVEN> <FAMILY>Morali</FAMILY> Esq.</NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>Mr. <GIVEN>Henri</GIVEN> L. <FAMILY>Belolo</FAMILY>, M.D.</NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>Mr. <GIVEN>Victor</GIVEN> C. <FAMILY>Willis</FAMILY></NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME>Mr. <GIVEN>Jacques</GIVEN> S. <FAMILY>Morali</FAMILY></NAME>
  </PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Declaring Mixed Content

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="PersonType">
    <xsd:element name="NAME">
      <xsd:complexType content="mixed">
        <xsd:element name="GIVEN"  type="xsd:string" 
          minOccurs="1" maxOccurs="1"/>
        <xsd:element name="FAMILY" type="xsd:string" 
          minOccurs="1" maxOccurs="1"/>      
      </xsd:complexType>
    </xsd:element>
  </xsd:complexType>

  <xsd:complexType name="SongType" content="elementOnly">
  
    <xsd:element name="TITLE"     type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="PHOTO"     type="PhotoType"  
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="COMPOSER"  type="PersonType" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="PersonType" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="YEAR"   type="xsd:year" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="ARTIST" type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    
  </xsd:complexType>

  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>
  
</xsd:schema>

When Order Doesn't Matter

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="unordered_song.xsd">
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>
    <NAME><FAMILY>Morali</FAMILY> <GIVEN>Jacques</GIVEN></NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME><GIVEN>Henri</GIVEN> <FAMILY>Belolo</FAMILY></NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME><FAMILY>Willis</FAMILY> <GIVEN>Victor</GIVEN></NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME><GIVEN>Jacques</GIVEN> <FAMILY>Morali</FAMILY></NAME>
  </PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

The xsd:all Group

Each element in the xsd:all group must occur zero or once; that is minOccurs and maxOccurs must each be 0 or 1
The xsd:all group must be the top level element of its type
The xsd:all group may contain only individual element declarations; no choice or sequences

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="PersonType">
    <xsd:element name="NAME">
      <xsd:complexType>
        <xsd:all>
          <xsd:element name="GIVEN"  type="xsd:string" 
            minOccurs="1" maxOccurs="1"/>
          <xsd:element name="FAMILY" type="xsd:string" 
            minOccurs="1" maxOccurs="1"/> 
        </xsd:all>     
      </xsd:complexType>
    </xsd:element>
  </xsd:complexType>

  <xsd:complexType name="SongType">
      <xsd:element name="TITLE" type="xsd:string" 
        minOccurs="1" maxOccurs="1"/>
      <xsd:element name="PHOTO" type="PhotoType"  
        minOccurs="0" maxOccurs="1"/>
      <xsd:element name="COMPOSER" type="PersonType" 
        minOccurs="1" maxOccurs="unbounded"/>
      <xsd:element name="PRODUCER" type="PersonType" 
        minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="PUBLISHER" type="xsd:string" 
        minOccurs="0" maxOccurs="1"/>
  
      <xsd:element name="YEAR" type="xsd:year" 
        minOccurs="1" maxOccurs="1"/>

      <xsd:element name="ARTIST" type="xsd:string" 
        minOccurs="1" maxOccurs="unbounded"/>
  </xsd:complexType>

  <!-- An empty element -->
  <xsd:complexType name="PhotoType" content="empty">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>
  
</xsd:schema>

Choices

xsd:choice requires exactly one of a group of specified elements to appear
The choice can have minOccurs and maxOccurs attributes that adjust this from zero to any given number.

Sequences

xsd:sequence requires each child element it specifies to appear in the specified order
The sequence can have minOccurs and maxOccurs attributes that repeat each sequence zero to any given number of times.

Adding a Price

<?xml version="1.0"?>
<SONG xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="derived_song.xsd">
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>
    <NAME><FAMILY>Morali</FAMILY> <GIVEN>Jacques</GIVEN></NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME><GIVEN>Henri</GIVEN> <FAMILY>Belolo</FAMILY></NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME><FAMILY>Willis</FAMILY> <GIVEN>Victor</GIVEN></NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME><GIVEN>Jacques</GIVEN> <FAMILY>Morali</FAMILY></NAME>
  </PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
  <PRICE>$1.35</PRICE>  
</SONG>

Derived Types

Suppose you want a money type to specify that the PRICE element content must look like $1.35 or ¥11000
Derive this from the xsd:string type by restriction
Use a regular expression to specify the pattern

Regular Expressions

More or less Perl-like with some Unicode extensions
The money regular expression:
\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?

\p{Sc}

Any Unicode currency indicator; e.g. $, ¥, £, ¤, etc.

\p{Nd}
A Unicode decimal digit character

\p{Nd}+
One or more Unicode decimal digit characters

\.
The period character

(\.\p{Nd}\p{Nd})
A string with a period followed by two decimal digits like .35

(\.\p{Nd}\p{Nd})?
Zero or one strings of the form .35

The xsd:simpletype element

The base attribute specifies the type it's derived from
The name attribute specifies the name it will be referred to as
The pattern child element imposes the restriction

  <xsd:simpleType base="xsd:string" name="money">
    <xsd:pattern value="\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?"/>
  </xsd:simpleType>

The Price Schema

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:simpleType base="xsd:string" name="money">
    <xsd:pattern value="\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?"/>
    <!-- 
       Regular Expression:
       \p{Sc}             Any Unicode currency indicator; e.g. $, &#xA5, &#xA3, &#A4, etc.
       \p{Nd}             A Unicode decimal digit character
       \p{Nd}+            One or more Unicode decimal digit characters
       \.                 The period character
       (\.\p{Nd}\p{Nd})
       (\.\p{Nd}\p{Nd})?  Zero or one strings of the form .35
       
       This works for any decimalized currency. 
       
    -->
  </xsd:simpleType>

  <xsd:complexType name="SongType">
      <xsd:element name="TITLE"     type="xsd:string" 
        minOccurs="1" maxOccurs="1"/>
      <xsd:element name="PHOTO"     type="PhotoType"  
        minOccurs="0" maxOccurs="1"/>
      <xsd:element name="COMPOSER"  type="PersonType" 
        minOccurs="1" maxOccurs="unbounded"/>
      <xsd:element name="PRODUCER"  type="PersonType" 
        minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="PUBLISHER" type="xsd:string" 
        minOccurs="0" maxOccurs="1"/>
      <xsd:element name="YEAR"   type="xsd:year" 
        minOccurs="1" maxOccurs="1"/>
      <xsd:element name="ARTIST" type="xsd:string" 
        minOccurs="1" maxOccurs="unbounded"/>
      <xsd:element name="PRICE" type="money" 
        minOccurs="1" maxOccurs="1"/>      
      
  </xsd:complexType>

  <xsd:complexType name="PersonType">
    <xsd:element name="NAME">
      <xsd:complexType>
        <xsd:all>
          <xsd:element name="GIVEN"  type="xsd:string" 
            minOccurs="1" maxOccurs="1"/>
          <xsd:element name="FAMILY" type="xsd:string" 
            minOccurs="1" maxOccurs="1"/> 
        </xsd:all>     
      </xsd:complexType>
    </xsd:element>
  </xsd:complexType>

  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>
  
</xsd:schema>

Default Namespace

<?xml version="1.0"?>
<GREETING 
  xmlns="http://ibiblio.org/xml/schemas/greeting/"
  xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
  xsi:schemaLocation="http://ibiblio.org/xml/schemas/greeting/
                      greeting_defaultNS.xsd">
  Hello XML!
</GREETING>

The targetNamespace attribute

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema"
  targetNamespace="http://ibiblio.org/xml/schemas/greeting/"
>
 
  <xsd:element name="GREETING" type="xsd:string"/>

</xsd:schema>

A Song with a Namespace

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SONG xmlns="http://ibiblio.org/xml/namespace/song"
      xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:schemaLocation = 
       "http://ibiblio.org/xml/namespace/song namespace_song.xsd"
>
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

A Schema for a Document that Uses the Default Namespace

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema"
  xmlns="http://ibiblio.org/xml/namespace/song"
  targetNamespace="http://ibiblio.org/xml/namespace/song"
  elementFormDefault="qualified"
  attributeFormDefault="unqualified"
>
 
  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="SongType">
  
    <xsd:element name="TITLE" type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="PHOTO" type="PhotoType"  
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="COMPOSER"  type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="xsd:string" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>    
    <xsd:element name="YEAR" type="xsd:year" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="ARTIST" type="xsd:string" 
      minOccurs="0" maxOccurs="unbounded"/>
    
  </xsd:complexType>

  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>
  
</xsd:schema>

Multiple Namespaces, Multiple Schemas

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SONG xmlns="http://ibiblio.org/xml/namespace/song"
      xmlns:xlink="http://www.w3.org/1999/xlink"
      xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance"
      xsi:schemaLocation = 
       "http://ibiblio.org/xml/namespace/song namespace_song.xsd
        http://www.w3.org/1999/xlink xlink.xsd"
>
  <TITLE>Hot Cop</TITLE>
  <PHOTO xlink:type="simple" xlink:href="hotcop.jpg"
    ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

XLink Schema

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  targetNamespace="http://www.w3.org/1999/xlink"
  attributeFormDefault="qualified"
>

  <xsd:attributeGroup name="XLinkAttributes">
    <xsd:attribute name="xlink:simple" type="xsd:string"/>
    <xsd:attribute name="xlink:href"   type="xsd:uriReference"/>
  </xsd:attributeGroup>
  
</xsd:schema>

Song Schema with XLink Support

<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema"
  xmlns="http://ibiblio.org/xml/namespace/song"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  targetNamespace="http://ibiblio.org/xml/namespace/song"
  elementFormDefault="qualified"
  attributeFormDefault="unqualified"
>
 
  <xsd:import namespace="http://www.w3.org/1999/xlink" 
              schemaLocation="xlink.xsd"/>

  <xsd:complexType name="PhotoType">
    <xsd:complexContent>
       <xsd:restriction base="xsd:anyType">
         <xsd:attributeGroup ref="XLinkAttributes"/>
         <xsd:attribute name="ALT"    type="xsd:string"/>
         <xsd:attribute name="WIDTH"  type="xsd:nonNegativeInteger"/>
         <xsd:attribute name="HEIGHT" type="xsd:nonNegativeInteger"/> 
      </xsd:restriction>
    </xsd:complexContent>
  </xsd:complexType>

  <xsd:element name="SONG" type="SongType"/>

  <xsd:complexType name="SongType">
  
    <xsd:element name="TITLE"     type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="PHOTO"     type="PhotoType"  
      minOccurs="0" maxOccurs="1"/>
    <xsd:element name="COMPOSER"  type="xsd:string" 
      minOccurs="1" maxOccurs="unbounded"/>
    <xsd:element name="PRODUCER"  type="xsd:string" 
      minOccurs="0" maxOccurs="unbounded"/>
    <xsd:element name="PUBLISHER" type="xsd:string" 
      minOccurs="0" maxOccurs="1"/>    
    <xsd:element name="YEAR"   type="xsd:year" 
      minOccurs="1" maxOccurs="1"/>
    <xsd:element name="ARTIST" type="xsd:string" 
      minOccurs="0" maxOccurs="unbounded"/>
    
  </xsd:complexType>

</xsd:schema>

Annotations

The top-level xsd:annotation element describes the schema
Its xsd:documentation child element describes the schema for human readers
Its xsd:appInfo child element describes the schema for computer programs; e.g. stylesheet instructions

  <xsd:annotation>
   <xsd:documentation>
    Song schema for XML and Java Example at Software Development 2000 East
    Copyright 2000 Elliotte Rusty Harold. 
   </xsd:documentation>
  </xsd:annotation>

What Schemas don't do

Cannot declare entities
Parent models
Extra-document validation

Schema Alternatives

Rick Jelliffe's Schematron
Murato Makoto's RELAX
DTDs

Schematron

Rick Jelliffe's Schematron:
The Schematron differs in basic concept from other schema languages in that it not based on grammars but on finding tree patterns in the parsed document. This approach allows many kinds of structures to be represented which are inconvenient and difficult in grammar-based schema languages.
XSLT/XPath Based
http://www.ascc.net/xml/resource/schematron/schematron.html

RELAX

Murato Makoto
JIS standard
Uses W3C Schema data types
http://www.xml.gr.jp/relax/

DTDs aren't Dead!

To Learn More

This presentation: http://www.ibiblio.org/xml/slides/sd2000east/schemas/
W3C Schema Primer: http://www.w3.org/TR/xmlschema-0/
XML Schema Part 1: Structures: http://www.w3.org/TR/xmlschema-1/
XML Schema Part 2: Datatypes: http://www.w3.org/TR/xmlschema-2/

Questions?

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